CN111363167A

CN111363167A - Preparation method of RGO/HA/PVA shape memory hydrogel and product thereof

Info

Publication number: CN111363167A
Application number: CN202010151275.0A
Authority: CN
Inventors: 卢晓英; 魏立恒; 李冕; 卢怡; 宋华军; 雷志豪; 翁杰
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2020-03-06
Filing date: 2020-03-06
Publication date: 2020-07-03

Abstract

The invention discloses a preparation method of RGO/HA/PVA shape memory hydrogel and a product thereof, belonging to the technical field of hydrogel, wherein the RGO/HA/PVA hydrogel with uniform structure is successfully prepared by doping composite powder of HA and RGO into a PVA matrix through an in-situ growth method, the RGO/HA/PVA hydrogel HAs uniform structure, HA particles are uniformly dispersed in the PVA matrix, and the RGO/HA/PVA hydrogel HAs good thermal stability, compared with pure PVA, the tensile strength of the RGO/HA/PVA hydrogel is improved by 3 times, the elongation at break is increased by about 7 times, and the RGO/HA/PVA hydrogel HAs good shape memory performance under the condition of solvent (water and PBS solution) thermal induction stimulation.

Description

Preparation method of RGO/HA/PVA shape memory hydrogel and product thereof

Technical Field

The invention belongs to the technical field of hydrogel, and particularly relates to a preparation method of RGO/HA/PVA shape memory hydrogel and a product thereof.

Background

The PVA hydrogel prepared by the crosslinking method has large elastic modulus, good toughness and stable property, a crystalline region in a network structure of the PVA hydrogel is used as a stationary phase, an amorphous region is used as a reversible phase, and the PVA hydrogel has two essential elements necessary for shape memory, so the PVA hydrogel has a potential application prospect in the aspect of shape memory. Pure PVA has poor mechanical strength and shape memory performance, and the aim of improving the mechanical strength and the shape memory capacity of PVA hydrogel is realized by improving the physical crosslinking degree of a PVA network structure or adding inorganic particles for reinforcement. As a novel shape memory polymer, PVA and a composite material thereof are still in the initial stage of relevant research at present. Inorganic particle reinforced composite hydrogel has been studied more deeply, and various hydrogels with different purposes and different properties are developed successively, so that more research results are obtained. HA HAs chemical composition and crystal structure similar to those of human natural bone, and HAs good bioactivity and biocompatibility. Reduced Graphene Oxide (RGO) has excellent mechanical properties and a very high length-diameter ratio, also contains various oxygen-containing functional groups, is often used as a reinforcing phase to improve the mechanical strength of a matrix, and has no toxic or side effect as proved by cytotoxicity evaluation. However, the hydrogel in the prior art has poor stability, poor shape memory performance, poor recovery rate and unstable mechanical property.

In conclusion, under the condition of ensuring that the shape memory effect exists under multiple conditions of stimulation, the hydrogel with good mechanical properties needs to be researched.

Disclosure of Invention

Aiming at the problems, the invention aims to provide a preparation method of RGO/HA/PVA shape memory hydrogel and a product thereof.

In order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method of RGO/HA/PVA shape memory hydrogel comprises the following steps:

(1) preparing a PVA aqueous solution with the mass volume fraction of 8%;

(2) adding RGO/HA composite powder into PVA water solution, stirring uniformly, performing ultrasonic treatment for 0.5h, and standing overnight to remove bubbles;

(3) adding diluted HNO dropwise₃Adding into the mixed solution, adjusting pH value of the solution to 3.5, and standing at about 30 deg.C for 24 hr;

(4) dripping the Wuerdizao into the solution prepared in the step (3) for crosslinking, fully stirring uniformly, standing at room temperature until the crosslinking is complete to form gel;

(5) adding ammonia water above the gel prepared in the step (4) for mineralization, and recrystallizing to grow HA;

(6) and (5) after HA crystallization in the step (5) is finished, repeatedly washing the gel with deionized water to be neutral, and preparing the RGO/HA/PVA shape memory hydrogel.

Further, the step (1) of preparing the aqueous PVA solution comprises the following steps: dispersing PVA in water, after the PVA is completely soaked by the water, placing the beaker at a constant temperature of 60 ℃ and magnetically stirring until the PVA is completely dissolved.

Further, the preparation method of the RGO/HA composite powder of the step (2) comprises the following steps:

a: preparing a GO solution with the concentration of 0.5 mg/ml;

b: ca (NO) was weighed out separately in a Ca/P molar ratio of 1.67₄)₂·4H₂O and Na₂HPO₄·12H₂O, mixing with ureaDissolving in distilled water;

c: dropwise adding the solution prepared in the step B into the GO solution prepared in the step A, adding dilute nitric acid to adjust the pH to 3, and uniformly stirring;

d: transferring the mixed solution prepared in the step C into a hydrothermal reaction kettle, sealing and putting into an oven, heating to 180 ℃, and preserving heat for 2 hours;

e: and D, naturally cooling the hydrothermal reaction kettle after heat preservation in the step D, taking out a reaction product in the hydrothermal reaction kettle, centrifugally washing to be neutral, and drying at 60 ℃ to obtain the RGO/HA composite powder.

Further, the pH above the gel during the mineralization in step (5) is maintained at 11.

Furthermore, the product prepared according to the preparation method of the RGO/HA/PVA shape memory hydrogel HAs the mass percent of RGO in the hydrogel of 6.67 wt%.

The invention selects HA with good biocompatibility to improve the biocompatibility of the material, and RGO is used as a reinforcing phase to improve the mechanical property of the material, so that the HA and the RGO can be uniformly dispersed in a polymer matrix, and the RGO/HA composite powder is used for adding the HA and the RGO into the PVA matrix to prepare the RGO/HA/PVA composite hydrogel.

The Graphene Oxide (GO) solution used in the invention is prepared by an improved Hummers method. Then preparing RGO/HA composite powder by a hydrothermal reaction method so as to achieve the purposes of reducing GO and improving HA crystallinity. The RGO/HA composite powder prepared by the hydrothermal reaction method HAs high HA crystallinity, is tightly combined with RGO, is uniformly dispersed in the HA, is not added with any reducing agent to reduce the RGO, and does not have the residue of the reducing agent in the composite material.

The preparation method of the composite material is an in-situ growth method, the prepared RGO/HA composite powder and PVA aqueous solution are uniformly mixed to prepare gel, and then HA is grown in situ to obtain RGO/HA/PVA composite hydrogel. The pure PVA hydrogel HAs hydrogen bond effect of side chain hydroxyl combination between PVA and PVA, and after RGO/HA composite powder is added, the composite hydrogel with uniform structure is prepared by an in-situ growth method. At this time, Ca in HA²⁺Will form a coordination structure with the hydroxyl group in PVA, and-OH will form a coordination structure with PVAThe hydroxyl groups of (a) undergo hydrogen bonding. The oxygen-containing functional group (hydroxyl, carboxyl and the like) on the RGO also has hydrogen bond interaction with the hydroxyl on the PVA, and the RGO with high length-diameter ratio can also be intertwined with the molecular chain of the PVA to be used as an additional physical crosslinking point of the PVA. In the shape memory recovery process, after the composite hydrogel is placed in water, water molecules enter the hydrogel in succession and perform hydrogen bonding with each molecular group, such as hydroxyl, carboxyl and carboxyl on RGO, hydroxyl on PVA and PO in HA₄ ^3-And the energy storage modulus is a reflection of the internal energy of the polymer, so that the movement of molecular chains in the polymer is more easily initiated. In addition, it has been found that the hydrogen competition between water molecules and RGO also leads to a decrease in the internal storage modulus. The water molecule is immersed in the gel and can take place the hydrogen bond effect with hydroxyl, and the oxygen-containing functional group on the RGO also can take place the effect with hydroxyl to the effect of this kind of water molecule and RGO's competition hydrogen bond can reduce the hydrogen bond in the PVA network, weakens PVA network structure, reduces the inside energy storage of gel, and indirect just be equivalent to improving the material external energy, and the shape is replied and can be taken place, improves the deformation rate of recovery.

The invention has the beneficial effects that:

the invention successfully prepares the RGO/HA/PVA hydrogel with uniform structure by doping the composite powder of HA and RGO into the PVA matrix through an in-situ growth method, and HA particles are uniformly dispersed in the PVA matrix and have good thermal stability; compared with pure PVA, the tensile strength of the RGO/HA/PVA hydrogel is improved by 3 times, and the elongation at break is increased by about 7 times; the RGO/HA/PVA hydrogel HAs good shape memory performance under the condition of solvent (water and PBS solution) heat-induced stimulation, and the final deformation recovery rate of the hydrogel is high.

Drawings

FIG. 1 is an XRD pattern of different composite hydrogels;

figure 2 is a graph of the grain size of HA at 2 θ -32 ° and the crystallinity of PVA in different composite hydrogels;

FIG. 3 is a FT-IR spectrum of various composite hydrogels;

FIG. 4 is a DSC curve (top) and TG curve (bottom) of different composite hydrogels;

FIG. 5 is a stress-strain curve (a) for various composite hydrogels;

FIG. 6 is the tensile mechanical properties (b) of different composite hydrogels;

FIG. 7 shows the tensile test results for various composite hydrogels;

FIG. 8 is a graph showing the shape recovery and the time required for different composite hydrogels under water-induced conditions.

Detailed Description

In order to further illustrate the technical effects of the present invention, the present invention is specifically described below by way of examples.

Example 1

Preparing RGO/HA composite powder by a hydrothermal method:

the RGOHA composite powder prepared by the hydrothermal reaction method HAs high HA crystallinity, is tightly combined with RGO, is uniformly dispersed in the HA, does not add any reducing agent to reduce the RGO, and does not have the residue of the reducing agent in the composite material. The specific preparation process comprises the following steps:

1) preparing the GO solution into a volume concentration ratio of 0.5mg/ml, and fully and uniformly stirring;

2) respectively weighing Ca (NO) with corresponding mass according to the Ca/P molar ratio of 1.67₄)₂·4H₂O and Na₂HPO₄·12H₂Dissolving the mixed urea in distilled water;

3) dropwise adding the uniformly mixed solution into the prepared GO solution, adding dilute nitric acid to adjust the pH value until the pH value of the mixed solution is 3, and fully and uniformly stirring;

4) transferring the mixed solution into a hydrothermal reaction kettle, sealing and putting into an oven, heating to 180 ℃, and preserving heat for 2 hours;

5) and naturally cooling, taking out a reaction product in the hydrothermal reaction kettle, centrifugally washing to be neutral, drying at 60 ℃, and storing in a drying tower for later use.

Preparing RGO/HA/PVA shape memory hydrogel by an in-situ growth method:

1) preparing an 8% PVA aqueous solution (4 g of PVA is dispersed in 50ml of water, after the PVA is completely soaked by the water, a beaker is placed on a magnetic stirring device at a constant temperature of 60 ℃ until the PVA is completely dissolved);

2) adding a proper amount of RGO/HA composite powder into a PVA aqueous solution, uniformly stirring, performing ultrasonic treatment for 0.5h, and standing overnight to remove bubbles;

3) dropwise adding diluted HNO3 into the mixed solution, adjusting the pH value of the solution to about 3.5, and standing for 24h at about 30 ℃;

4) dripping 1ml of glutaraldehyde into the mixed solution for crosslinking, fully and uniformly stirring, and standing at room temperature until the crosslinking is complete to form gel;

5) adding ammonia water above the gel for mineralization, recrystallizing and growing HA, but keeping the pH value above the gel at about 11;

6) and after HA crystallization is finished, repeatedly washing the gel with deionized water to be neutral, putting the gel into water, and storing for later use.

And (3) analyzing an experimental result:

1.1X-ray diffraction (XRD) analysis

Cutting the composite material into slices with the length of 30mm, the width of 20mm and the thickness of 1mm, drying the slices in a vacuum drying oven at 60 ℃, and performing phase analysis and hydrogel crystallization analysis on the composite material by using an X-ray diffractometer, wherein the measurement parameters are as follows: the copper target was scanned at a speed of 10 °/min and at diffraction angles in the range of 10-80 °, as shown in fig. 1.

Diffraction peaks of PVA have diffraction angles (2 theta) mainly near 19.5, 22.8 degrees and 40.6 degrees; diffraction angles (2 θ) of diffraction peaks of the HA crystal mainly appear in the vicinity of 26 °, 32 °, and the like. As shown in fig. 1, XRD diffraction patterns of the different composite hydrogels. It can be seen that the XRD patterns of the various composite hydrogels all show the characteristic peaks of the PVA and HA components, and the crystallinity and the grain size are respectively shown in fig. 2 by calculation of the JADE software.

The diffraction characteristic peak grain size of the HA in the HA/PVA composite hydrogel at 2 theta (32 ℃) is about 23.03nm and is larger than 17.37nm in the RGO/HA/PVA composite hydrogel, which shows that the crystallinity of the HA in the HA/PVA hydrogel is better than that of the RGO/HA/PVA hydrogel. The diffraction peak of the PVA at 2 θ of 19.5 ° of RGO/HA/PVA hydrogel was weaker than that of the pure PVA hydrogel in widening the peak shape, and showed a certain disorder, and it is understood from fig. 2 that the crystallinity of PVA decreased after the addition of RGO, which indicates that the addition of RGO affects the crystallinity of PVA, because the RGO with high aspect ratio was entangled with the molecular chain of PVA and also the combination of hydrogen bonds, so that the arrangement of PVA segments was partially disordered and the crystallinity was decreased. The reason why the RGO contained in the composite material does not have any peak in XRD is that the RGO has good dispersibility, so that it assumes a uniformly dispersed state, which is also the reason why there is no characteristic peak of RGO.

1.2 Fourier transform Infrared Spectroscopy (FT-IR)

Cutting the composite material into pole pieces with the length of 20mm, the width of 10mm and the thickness of 0.5mm, drying in a vacuum drying oven at 60 ℃, and detecting the functional groups and chemical compositions of the composite material by an infrared spectrometer.

PVA is cross-linked by glutaraldehyde to generate intramolecular or intermolecular cross-linking, and the groups contained in the added HA and RGO can also generate the combination and hydrogen bond interaction with PVA chains. As shown in fig. 3, FTIR spectra of different composite hydrogels, and analysis shows that HA-related peaks are probably: an absorption peak at 1637cm-1 is H₂Bending vibration of-OH in O, PO₄ ^3-Characteristic band of (2) is located at 1033cm^-1And 604cm^-1，565cm^-1Nearby is HPO₄ ^2-And PO₄ ^3-Multiple absorption peaks overlap. These characteristic peaks can be found on the infrared spectra of both RGO/HA composite powder and composite hydrogel. wherein-OH bending vibration peaks on different composite hydrogels (HA/PVA and RGO/HA/PVA) are blue-shifted, which shows that hydroxyl on HA and hydroxyl on PVA chain are subjected to hydrogen bond action, and the stability of-OH is improved; different composite hydrogels were at 1033cm^-1、604cm^-1、565cm^-1PO of₄ ^3-The peak intensity of the characteristic peak is obviously weakened, the RGO/HA/PVA hydrogel is weaker than the HA/PVA hydrogel, but the RGO/HA of the composite powder is not obviously changed, which shows that the PO group and the hydroxyl on the side chain of the PVA also have hydrogen bond action, and the PO-group vibration is weakened. PVA is a polyhydroxy macromolecule, and the main characteristic absorption peaks of PVA are as follows: at 3000-3600cm^-1Within a range of a relatively specific broad absorptionPeak, which is-OH stretching vibration peak, 2941cm^-1Is C-H stretching vibration peak, 1375cm^-1、1244cm^-1Is CH₂Or the vibrational peak of the C-H group, 1095cm^-1Is the C-O bond stretching vibration peak. The PVA related vibration peak appears in different composite hydrogels, and is 1375cm^-1、1244cm^-1CH of (A)₂Or the vibrational peak of the C-H group is blue-shifted and 1095cm in the RGO/HA/PVA hydrogel^-1Compared with HA/PVA hydrogel, the C-O bond stretching vibration peak is stronger, which shows that not only the added HA and the hydroxyl action of the PVA molecular chain influence the group vibration of the molecular chain, but also the oxygen-containing functional group on the RGO and the PVA molecular chain generate hydrogen bond action, so that the group vibration between the molecular chains is more stable, and the PVA matrix HAs stable internal motion.

1.3 thermal Property analysis

The thermal stability of the composite hydrogels was tested with a differential scanning calorimeter (NETZSCHRSTA 449-F3). All samples are 8-10 mg in weight, the detection temperature is 20-700 ℃, the heating rate is 20 ℃/min, and nitrogen is introduced for protection.

It can also be seen from FIG. 4 that the thermal curves of the RGO/HA/PVA hydrogels all shifted toward high temperatures, indicating that the addition of RGO can improve the thermal stability of the material. In the TG diagram of FIG. 4 (bottom), the sample no longer lost weight from 500 ℃ and the residual amount of RGO/HA/PVA hydrogel was higher than that of HA/PVA hydrogel because the PVA content in HA/PVA hydrogel was relatively higher in the equivalent mass comparison, and thus the weight loss due to thermal decomposition, carbonization, and the like of PVA was higher.

1.4 analysis of tensile Properties

In order to compare the mechanical strength of the composite material added with HA and RGO, the composite hydrogel is cut into thin strips with the length of 40mm, the width of 10mm and the thickness of 1mm, the strips are dried for 24 hours at room temperature to ensure that the water content of the composite hydrogel is the same, and a universal mechanical testing machine is used for testing the tensile strength of a sample.

FIG. 5 is a tensile stress strain curve for various composite hydrogels. As is clear from the figure, the mechanical strength of the composite hydrogel increases with the addition of HA and RGO, and the addition of RGO can greatly improve the strength of the hydrogel. When stress is applied to the composite hydrogel, load is mainly born by matrix macromolecules, when HA particles and RGO are dispersed on a chain segment of the matrix macromolecules, the movement of the matrix macromolecules is limited, and the RGO with high length-diameter ratio is easy to be wound with a PVA chain to block the movement of the chain segment, so that the tensile strength of the composite hydrogel can be improved by adding the HA and the RGO, and the tensile strength can be improved by compounding with a second phase. FIG. 6 and FIG. 7 show the results of tensile test analysis of different composite hydrogels. The tensile strength and the fracture toughness of the RGO/HA/PVA hydrogel are obviously higher than those of pure PVA and HA/PVA hydrogel, the tensile strength is improved to 0.18MPa from 0.06MPa, the tensile strength is increased by three times, the elongation at break is improved to 254 percent from 37 percent, and the elongation at break is increased by about 7 times. On one hand, the RGO can be wound with a PVA chain to form a stable cross-linking point, and when the RGO is stretched by external force, the RGO can not only block the motion of the PVA chain segment, but also play a role in fixing the molecular chain; on the other hand, it is possible that the size of the HA particles in the RGO/HA/PVA hydrogel is larger than that in the HA/PVA hydrogel, and as can be seen from the SEM results, the sizes of the HA particles in the HA/PVA hydrogel and the RGO/HA/PVA hydrogel are about 895nm and 3um respectively, and the size of the HA particles in the RGO/HA/PVA hydrogel is three times larger than that in the RGO/HA/PVA hydrogel. The larger the HA particles in the composite hydrogel, the greater the resistance to the motion of the PVA chain segment, and more external force is required for the motion of the PVA chain. However, the elastic modulus of RGO/HA/PVA hydrogels is lower because the addition of RGO increases the disorder degree of the PVA molecular chains, decreases the crystallinity of PVA, and thus the elastic modulus is lower.

1.5 relationship between recovery time and shape recovery ratio of different composite hydrogels under water induction condition

In this example, 70 ℃ was selected as the temperature for shape memory softening of the sample, and during the softening process, the hydrogel material lost water, and it was known that the completely dried hydrogel swelled back into water and returned to its original shape before drying. Therefore, in this design, the composite hydrogel is put into water to perform a shape memory recovery experiment, the operation is performed at room temperature, the sample is cooled and solidified and then recovers the shape in water, and the relationship between the deformation recovery rates of different composite hydrogels and the time is studied, as shown in fig. 8 (the shape recovery rates of different composite hydrogels under the water induction condition and the required time).

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and although the technical solutions of the present invention are described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A preparation method of RGO/HA/PVA shape memory hydrogel is characterized by comprising the following steps:

(1) preparing a PVA aqueous solution with the mass volume fraction of 8%;

2. The method of preparing the RGO/HA composite powder of step (2), according to claim 1, comprising the steps of:

a: preparing a GO solution with the concentration of 0.5 mg/ml;

b: ca (NO) was weighed out separately in a Ca/P molar ratio of 1.67₄)₂·4H₂O and Na₂HPO₄·12H₂O, mixing urea and fully dissolving in distilled water;

3. The method of claim 1, wherein the pH above the gel during the mineralization in step (5) is maintained at 11.

4. An RGO/HA/PVA shape-memory hydrogel prepared by the preparation method according to any one of claims 1 to 3.

5. The RGO/HA/PVA shape-memory hydrogel of claim 4 wherein the mass percent of RGO in the hydrogel is 6.67 wt%.